I don't think, short of Sauron's actual presence, the orcs would or could have attacked the balrog. I believe the balrog would have exercised an influence on the orcs that I don't think even the Nazgul would have been able to overcome.

So if Sauron himself stayed out of it, the Balrog could be more powerful than the Nazgul? And beat them in a streight fight? That is an interesting idea